In the art of oilfield drilling technology "directional drilling" is becoming increasingly prominent. In directional drilling the angle of the borehole is altered during the drilling operation from vertical toward horizontal. Initially directional drilling was developed in order to explore for oil under natural barriers such as lakes. However, it has been determined that if the borehole passes along rather than merely vertically traverses a permeable oil bearing formation a dramatically increased flow rate can be obtained. When directional drilling was in its infancy, the "bent subs" used were merely sections of drill string machined to have a preselected angular offset. This required a plurality of bent subs to be kept on site as a range of angular offsets were required. As the art advanced bent subs were developed which could be adjusted to a variety of angular offsets eliminating the need for a plurality of bent subs. An example of such an adjustable bent sub developed by the Applicant is Canadian Patent 1,243,663.
At the present time persons skilled in the art of directional drilling when high angle or horizontal holes are drilled to place two bent subs in the drilling motor assembly. The reason two are used is to permit an increased angle to be obtained. To go from a vertical to a horizontal hole it is often required to "build angle" very quickly. It is generally viewed as desirable to place the bent subs as close to the drill bit as possible. One bent sub is generally positioned between the downhole drilling motor and the bearing assembly, and the other is generally placed above the downhole drilling motor. Whenever two bent subs are used an additional problem is created. The bent subs must be orientated with respect to each other in order that the angular offset created is cumulative. Initially, the orientation of the bent subs was achieved through the use of an "orientation sub", which was well known in the art. An orientation sub, as its name implies, has one component which can rotate in relation to a mating component in order to orientate the drill string. As previously stated it is desirable to have the bent subs as close to the drill bit as possible. The use of an orientation sub added to the length of the drilling motor assembly; for this reason, the use of orientation subs in this application has been abandoned in favor of a plurality of "shims" between the shoulders of the threaded connection at the motor and bent sub. The obvious advantage of using shims is that they do not add appreciably to the length of the drilling motor assembly. However, there are a number of obvious disadvantages in orientating the bent subs using shims; such as the time required for adjustment.